1. Field of the Invention
The present invention relates to a consumable electrode arc welding method. In particular, the present invention relates to constriction detection control and wire feed rate variable control in a consumable electrode arc welding method.
2. Description of the Related Art
JP-A-2006-281219 discloses a technique related to consumable electrode arc welding. In the conventional consumable electrode arc welding, an arc generating state and a short-circuiting state repetitively occur between a welding wire and a base material. As a premonitory sign of regeneration of an arc from a short-circuiting state, a constriction forms in a molten droplet. The formation of a constriction is detected based on a change in the voltage (or resistance) between the welding wire and the base material. When a constriction is detected, the welding current is reduced sharply so that an arc is generated in a low current. This constriction detection control reduces spattering during arc generation.
JP-A-7-51854 discloses a technique of variably controlling the feed rate of a welding wire to keep the welding current constant even when the distance between a power supply chip and the base material (hereinafter referred to as “chip-base distance”) changes. Generally, the penetration depth of the base material is substantially proportional to the welding current. Thus, when the welding current is constant, the penetration depth is kept uniform, which leads to high welding quality. In ordinary arc welding, welding is performed with the chip-base distance kept constant. However, in the welding with a deep groove or multi-pass welding, it may be difficult to keep the chip-base distance constant due to e.g. problems such as contact of the welding torch and the base material. Even when the chip-base distance needs to be changed in this way, the technique disclosed in JP-A-7-51854 makes it possible to keep the welding current constant by variably controlling the feed rate, thereby preventing the penetration depth from varying.
In performing welding, both of the above-described feed rate variable control and constriction detection control can be employed at the same time. However, when the feed rate is rapidly changed by variable control, the state of constriction formed in a molten droplet changes. This hinders proper constriction detection control and results in unstable welding state. Conventionally, therefore, when feed rate variable control is performed, constriction detection control is not performed, which, however, increases the spattering.